Electric valve converting system



June 17, 1941. c. c. HERSKIND ELECTRIC VALVE CONVERTING SYSTEM Filed001:. 3, 1939 ull-III.

v/ w m r n .1 m m e t vC M M 5 .H i y b Patented June 17, 1941 2,246,173ELEGTRIC VALVE CONVERTING SYSTEM Carl C. Herskind, Schenectady, N. Y.,assignor to General Electric Company, a corporation of New YorkApplication October 3, 1939, Serial No. 297,694 9 illaims. :(Cl.175-363) My invention relates to electric valve converting systems andmore particularly to a control system for insuring load division betweenparallel operated electric valve devices of the type which are providedwith means for compensating for natural regulation.

In the operation of electric valve converting apparatus it has beenfound desirable from the standpoint of economical construction,eificiency of operation and reliability of service to divide theapparatus into a number of parallel connected units, preferably each ofthe units being of substantially the same capacity.

It is well known that any electric valve converting apparatus or asystem including transformer windings, electric valves, etc., has acertain amount of natural regulation; that is, a certain drop in voltageupon increase in the load current from no load to a full load due to theimpedance of the system. In order to compensate for this naturalregulation characteristic, electric valve converting systems have beenprovided with means to tend to increase the average voltage impressedupon the load circuit with increasing load in order to compensate forthe natural regulation of the system.

However, in the operation of parallel connected valve devices of thetype provided with means for compensating for natural regulation it isfound that one or more of the valve devices or converter units has atendency to assume more than itsproportionate share of the total loadhandled by the electric valve converting system; in fact without someprovision there is a tendency for one of the units to carry all of theload. This resulting unbalance in the load produces many undesirableconditions. Not only does it limit the total output of the electricvalve converting system but it may seriously endanger the reliableoperation of the apparatus besides producing undesirable harmonics andload conditions in the supply circuit of the converting system.

It is an object of my invention, therefore, to overcome thedisadvantages above noted in connection with the parallel operation ofelectric valve devices which are provided with means for compensatingfor natural regulation.

It is another object of my invention to provide a new and improvedelectric valve converting system.

It is a further object of my invention to provide a control system foran electric valve converting system which will compel an equal loaddivision among the different units of the converting system.

. ence to the Still another object of my invention is to provide anelectric valve converting system provided with a plurality of parallelconnected units each of the type that compensates for natural regulationwith means which will compel each of the parallel connected units toassume its proportionate share of the load.

In accordance with the illustrated embodiment of my invention I providean electric valve converting apparatus for transmitting energy in eitherdirection .between direct and alternating current circuits. The electricvalve converting apparatus comprises a plurality of multi-valve arcdischarge devices, each provided with means for compensating for thenatural regulation of the system, and arranged to operate in parallelrelationship between the direct and alternating current circuits. Themeans for compensating for natural regulation comprises impulse transinaccordance with the varying load. In order to insure division of loadbetween the parallel operating units an equalizer bus is providedconnecting the saturating windings in parallel relationship so that thephase of the excitation potentials of the control circuits may be variedin exactly the same way on all of the parallel connected units.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, will best be understood by referfollowing descriptiontaken in connection with the accompanying drawing, in which Fig. 1 is adiagrammatic representation of an electric valve converting apparatus towhich my invention has been applied; while Fig. 2 is a modiiication ofthe embodiment illustrated in Fig. 1.

Referring now to Fig. 1 of the drawing I have illustrated therein anelectric valve converting apparatus for transmitting energy between athree phase alternating current circuit l0 and a direct current circuitl I Although my invention is applicable to any of the electric valveconverting systems well known in the art, whether converting from directto alternating current or vice versa, and whether the alternatingcurrent circuit is a single phase or polyphase circuit, for simplicityof disclosure I have illustrated an arrangement for transmitting energybetween three phase alternating current circuit to and direct currentcircuit ll. Also in order to simplify the following explanation theconverting apparatus will be described as transmitting energy fromalternating current circuit Ii] which will be termed the supply circuit,to direct current circuit II which will be termed the load circuit. Itwill be understood by those skilled in the art that the reverseconditions might equally well be true since the apparatus is readilyadaptable for energy transmission in the other direction.

Alternating current supply circuit I9 and direct current load circuit IIare interconnected by means of a plurality of separate electric valveconverter units I2 and I3 operating in parallel relationship. Theconverter unit I2 comprises a transformer it having its primary windingI5 connected to the three phase alternating current supply circuit It,and a plurality of Y-connected secondary networks it and I! inductivelyassociated with primary winding I5. An electric discharge device I8 isprovided with a plurality of substantially independent discharge pathseach provided with'an anode I9. These anodes I9 are connected,respectively, to the terminals of the Y-connected networks I6 and H. Forsimplicity of disclosure only a single one of the terminals of networksI6 and IT has been illustrated as connected to its respective anode I9,but it will be understood by those skilled in the art that all of theterminals are connected to corresponding anodes. Electric dischargedevice it is also provided with a single pool type cathode 20, Theneutral terminals of networks It and Il are interconnected by means ofan interphase transformer 2! the midpoint of which is connected througha smoothing reactor 22 to the negative side of direct current circuit IIthrough one pole of reversing switch 23 and a plurality of windings 24,25 and 26, the purpose of which will be hereinafter described.- Thecathode of electric valve device I8 is connected to the positive side ofdirect current load circuit I! through circuit breaker '2] and the otherpole of reversing switch 23.

Similarly, converter It includes a transformer Iii provided with aprimary winding I5 associated with alternating current supply circuitIIJ and'a plurality of Y-connected secondary networks It and ll havingthe phase terminals thereof connected to the respective anodes I9 ofelectric valve device I8 provided with a single pool type cathode 2B.The neutral terminals of secondary networks i6 and H are interconnectedby means of an interphase transformer 2|, the midpoint of which isconnected through a smoothing reactor 22 to the negative terminal of thedirect current load circuit II through reversing switch 23', and aplurality of transformer windings 2t, 25' and 26 the purpose of whichwill be hereinafter described. The cathode 2B is connected to thepositive terminal of direct current load circuit II through circuitbreaker 2i and one pole of reversing switch 23. It is obvious,therefore, that electric valve converters I2 and I3 are connected inparallel relationship for transmitting energy between three phasealternating current supply circuit III and direct current load circuitII. Although I have described each of the converter units I2 and I3 asprovided with multi-anode, single-cathode electric valve devices I8 andI8, respectively, it will be understood by those skilled in the art thatthese valve devices I8 and I8 might each be replaced by a plurality ofseparate valves each having an anode, a cathode and a control electrodemounted within a single envelope. Any of the electric valves known tothe art may be used, although I prefer to use electric valve devices ofthe type containing an ionizable gas or a vapor.

Reversing switches 23 and 23' are provided in order to control thedirection of energy flow between direct current circuit H andalternating current circuit If], while circuit breakers 21 and 2! areprovided in order that one or the other of the converters I2 or i3 maybe disconnected when the load is such that only a single unit sumces totransmit the electrical energy between circuits It and l I.

In order to control the operation of the converters l2 and I3 each ofthe electric valve devices I8 and iii are provided with a plurality ofgrids or control electrodes 28 and 28', respectively, associated withthe anodes I 9 and I9. The control electrodes 23 and 28' are part ofsuitable control circuits 29 and 2t, respectively. Since these controlcircuits are identical in every respect only the control circuit 2% willbe described. The corresponding parts of control circuit 253' will becharacterized by the same reference numerals as control circuit 29except that the reference numerals will be marked with a prime. Controlcircuit 29 comprises a suitable control transformer 38 upon whichcontrol potentials from a suitable source are impressed. Thistransformer is provided with a primary winding 3| and a secondarywinding 32. The control potentials impressed on primary winding iii ofcontrol transformer 36 may be obtained from any suitable source, and asillustrated for rectifier operation, when energy is transmitted fromalternating current supply circuit It to direct current load circuit IIprimary winding iii of control transformer 38 may be connected directlyto alternating current circuit Iil. If on the other hand, energy isbeing transmitted from direct current I I to alternating current circuitIll these control potentials may still be obtained satisfactorily fromalternating current circuit Ill if alternating current circuit Ii! isconnected to an independent source of electromotive force to determinethe frequency thereof.

The control potentials from secondary winding 32 are impressed through asuitable rotary phase shifting transformer 33 upon the primary windings34, 35 and 3B of a plurality of grid transformers having suitable coremembers 31, 38 and 38, respectively, schematically illustrated inFig. 1. Inductively associated with primary windings 34, 35 and 36 aresecondary windings 40, ll and 62, respectively, the end terminals ofwhich are suitably connected through current limiting resistors 63 tothe control electrodes or grids 28..

For simplicity of disclosure only one of the terminals of secondarywindings ill, 4i and 42 has been illustrated as connected to itsrespective control electrode 28, but it will be understood by thoseskilled in the art that each of the terminals is connected to itsrespective control electrode or. grid 28. The midpoints of secondarywindings All, GI and d2 of the grid transformers are connected through asuitable bias battery 44 to the cathode 2t of electric valve device I8.The cores 31, 3S and 39 of the grid transformers are preferably of thetype arranged to be saturated during a portion of the alternatingcurrent cycle so that potentials of peaked wave form may be impressedupon the control electrodes 28 as will be understood by those skilled inthe art.

In order to compensate for the natural regulation, that is, the drop involtage of the rectifier output with increase in load, the grid transinthe cycle of the alternating potential of supply circuit ID at which theresultant fluxes in the saturable cores 31, 38 and 39 of the respectivegrid transformers reverse polarity, which corresponds to the instants atwhich peaked impulses are supplied to the secondary windings 49, 4| and42. In this manner the excitation peaks or impulses impressed on thecontrol electrodes 28 are advanced in phase with increasing load currenton the system thus tending to increase the average voltage impressedupon the load circuit II and thus compensating for the naturalregulation of the system.

In order to prevent converter I2 or I3 from carrying more than itsproportionate share of the load, which is very likely among parallelconnected converter units provided with means for compensating fornatural regulation, I provide equalizer busses 45 and 45 whichinterconnect respectively the input and output terminals of seriallyconnected saturating windings 24, and 26 of converter I2 with the inputand output terminals of serially connected saturating windings 24', 25'and 26 of converter I3 so that these two sets of windings are connectedin parallel relation. Equalizer bus 45 interconnects the correspondingterminals of saturating windings 24 and 24 while equalizer bus 46interconnects the corresponding terminals of saturating windings 26 and23. By this arrangement the saturating windings of the converters I2 andI3 are connected in parallel and since they are designed to have thesame impedance substantially identical currents will flow through thesewindings of the respective converters thus insuring that regardless ofthe load on the converting system each of the converters I2 and I3 willcarry its proportionate share of this load. Switches 41 and 4? areprovided so that the equalizer busses 45 and 46 may be taken out ofoperation, it being understood of course that when only one of theconverters I2 or I3 is operating these switches will be in the openposition.

The operation of the electric valve converting apparatus illustrated inFig. 1 will be understood by those skilled in the art and only a briefdiscussion will be included herewith. When energy is transmitted fromalternating current circuit ID to direct current circuit II andconverters I2 and I3 are operating in parallel, switches 23 and 23' willbe in the position indicated in the drawing and circuit breakers 21 and21' will be in their closed positions. The phase shifting transformers33 and 33' of the converters I2 and I3 are adjusted so as to produce thedesired potential at load circuit II. The control circuits 29 and 29'will cause excitation potentials of peaked wave form to be impressed onthe control electrodes 28 and 29 so as to render the respective anodesI9 and I9 and the associated discharge paths conductive in propersequence whereby electrical energy will be transmitted through dischargedevices I8 and I8 from alternating current supply circuit 19 to directcurrent load circuit II. As the load on direct current circuit IIincreases, more current will flow through saturating windings 24, 25, 26and 24, 25', 26', tending to advance the phase of the grid excitationand thus tending to raise the voltage of direct current circuit H whichnormally would tend to decrease with increasing load due to theimpedance of the system. In order to insure an equal load devisionbetween the converters I2 and I3 switches 41 and 41' associated withequalizer busses 45 and 46 are closed so that direct current saturatingwindings 24, 25 and 26 of the grid transformers of converter I2 areconnected in parallel with the direct current saturating windings 24',25 and 26 of the grid transformers of converter I3 so that the samephase advance or retardation of the grid potential will occur in each ofthe parallel connected converters I2 and I3. By means of equalizerbusses 45 and 46 the direct current flowing through the saturatingwindings of the grid transformers of converters I2 and I3 are alwaysequal thus preventing one or the other of the converter units fromcarrying more than its share of the load.

Although I have described the apparatus illustrated in Fig. 1 asoperating to transmit energy from alternating current supply circuit Into direct current load circuit II, it will be understood that the systemwill operate equally well as an inverter in which case reversingswitches 23 and 23 are moved to their other positions and direct currentcircuit II becomes the supply circuit while alternating current circuitIll becomes the load circuit.

In the modification according to Fig. 2 only a portion of the electricvalve converting apparatus illustrated in Fig. 1 is shown and thecorresponding parts are designated by the same reference numerals.Electric converter apparatus I2 is provided with an equalizer coil 48connected across interphase transformer 2I while converting apparatus I3is provided with an equalizer coil 48 connected across interphasetransformer 2|. The midpoints of equalizer coils 48 and 48' areinterconnected by means of equalizer bus 49 and switches 59 and 50'. Bythis arrangement the currents flowing through reactors 22 and 22 andfrom there through the saturating coils of the grid transformers (notshown) are equalized so that each of the converters l2 and I3 will carryits prortionate share of the load. The midtaps of equalizer coils 48 and48 will be at a positive potential with respect to the negative bus ofload circuit II due to the potential drop in the interphase transformerby virtue of the load current. Inasmuch as the voltage drop between themidtap of the equalizer coil and the negative load bus is proportionalto the load on the rectifier a regulating potential may be obtainedacross the equalizer bus 49 and the negative bus of load circuit II, asfor example, from the circuit 5I which may be used for energizing thecompensating coil of a voltage regulator (not shown). By thisarrangement, therefore, not only is the load equalized betweenconverter-s I2 and I3, but a very simple means is provided for obtaininga potential proportional to the load for energizing the compensatingcoil of a Voltage regulator.

The operation of the modification illustrated in Fig. 2 will beunderstood by those skilled in the art in view of the detaileddescription included above with respect to Fig. 1.

While I have described particular embodiments of my invention, it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from my invention, and I,therefore, aim in the appended claims to. cover all such changes andmodifications as fall within the true spiritand scope of my invention. L

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In an electric valve converting apparatus, a supply circuit, a loadcircuit, one of said circuits being an alternating current circuit, aplurality of parallel connected electric discharge devicesinterconnecting said circuits, a control circuit for each of saidelectric discharge devices of the type in which the phase of theexcitation is advanced with increasing load, and means for insuring anequal division of load among said parallel connected electric dischargedevices comprising an equalizing bus for equally advancing the phase ofthe excitation of each of said discharge devices with increasing totalload transmitted by said parallel connected electric discharge devices.

2. In an electric valve converting system, a supply circuit, a loadcircuit, one of said circuits being an alternating current circuit, aplurality of parallel connected arc discharge devices each having aplurality of substantially independent arc paths for transmitting energybetween said circuits, a control electrode in each of said arc paths,excitation apparatus comprising a control circuit associated with saidelectrodes. for each of said are discharge devices including a saturablecore transformer for exciting said control electrodes with alternatingpotentials of peaked wave form, means for variably saturating the coresof said transformer in response to load current of the system so as toregulate the energy transmitted from said supply to said load circuit,and means for equalizing the load on each of said parallel connected arcdischarge devices comprising means for equally saturating the cores ofall of said transformers.

3. In an electric valve converting system, a supply circuit, a loadcircuit, one of said circuits being an alternating currentcircuit, aplurality of parallel connected arc discharge devices for transmittingenergy between said circuits, excitation apparatus comprising a controlcircuit including a saturable core transformer for each of said aredischarge devices, means for energizing said transformers with analternating potential of the frequency of said alternating currentcircuit, means for variably saturating the core or" said transformers inresponse to load current of the system so as to regulate the energytransmitted from said supply to said load circuit, and means forinsuring an equal division of load among said parallel connected arcdischarge devices comprising means ior producing an equal saturation ofthe cores of all of said transformers.

4. In an electric valve converting apparatus, a supply circuit, a loadcircuit, one of said circuits being an alternating current circuit, aplurality of parallel connected electric discharge devicesinterconnecting said circuits, a control circuit for each or" saidelectric discharge devices of the type in which the phase of theexcitation is advanced with increasing load, and means including aplurality of equalizer coils and an equalizer bus. for insuring an equaldivision of load among said parallel connected discharge devices.

5. In an electric valve converting system, a supply circuit, a loadcircuit, one of said circuits being an alternating current circuit, aplurality of parallel connected arc discharge devices each having aplurality of substantially independent arc paths for transmitting energybetween said circuits, a transformer for each of said parallel connectedarc discharge devices comprising a plurality of secondary windingsinterconnected by means of an interphase transformer, a controlelectrode in each of said are paths, excitation apparatus comprising acontrol circuit associated with said electrodes for each of said aredischarge devices including a saturable core transformer for excitingsaid control electrodes with alternating potentials of peaked wave form,means for variably saturating the cores of said transformer in responseto. load current of the system so as to regulate the energy transmittedfrom said supply to said load circuit, and means including an equalizercoil connected across each of said interphase transformers and anequalizer bus for equalizing the load on each of said parallel connectedelectric discharge devices so as tov equally saturate the cores of allof said transformers.

6. An electrical conversion system comprising two parallel connected arcdischarge devices interconnecting a direct current circuit and analternating current circuit, each of said are discharge devices having aplurality of substantially independent arc paths, control electrodesassociated With each of said are paths, an impulsing device associatedwith each of said are discharge devices for supplying control impulsesto the control electrodes of said devices, said impulsing devicescomprising saturable core transformers for producing alternatingpotentials of peaked Wave form, means for variably saturating the coresof said transformers in response to current flowing in said directcurrent circuit of said discharge devices, and means for equalizing theload be tween said two parallel connected arc discharge devicescomprising means for equally saturating the cores of the associatedimpulse transformers.

7. In an electric valve converting apparatus, a supply circuit, a loadcircuit, one of said circuits 7 being an alternating current circuit, aplurality of parallel connected electric discharge devicesinterconnecting said circuits, control electrodes and excitationcircuits therefor associated with each of said discharge devices to varythe excitation of said discharge devices in response to the currenttransmitted thereby between said supply and load circuits, and means forinsuring equal load division among said plurality of parallel connectedelectric discharge devices comprising 7 means for causing each of saidexcitation circuits to vary the excitation of each of said controlelectrodes in substantially identical manner.

8. In an electric valve converting apparatus, a supply circuit, a loadcircuit, one of said circuits being an alternating current circuit, apair of parallel connected discharge devices each having a controlelectrode associated therewith for controlling the initiation ofdischarge, a control circuit associated with each of said controlelectrodes for controlling theenergization thereof including means forimpressing a periodic voltthereon, means for varying the effective phaseof the voltage impressed on said control electrodes, and an equalizingconnection between the control circuits associated with each of saidcontrol members to insure equal load division between said parallelconnected electric discharge devices.

9. In an electric valve converting apparatus, 'a direct current circuit.an alternating current circuit, a pair of parallel connected arcdischarge devices each having a control member associated therewith, acontrol circuit associated with each of said control members and eachincluding a saturable inductive device for impressing on the 5 controlmember associated therewith a periodic voltage of peaked wave form, acontrol winding associated with each of said saturable inductive devicesfor controlling the phase of said periodic voltage, means for energizingsaid control winding to control the phase of said periodic voltage inresponse to an electrical condition to be controlled, and meansincluding an equalizing connection between the control windingsassociated with each of said parallel arc discharge devices for insuringdivision of load between said parallel connected arc discharge devices.

CARL C. HERSKIND.

